The disposal of sludges discharged from both municipal and industrial wastewater treatment plants continues to be a significant problem across the United States. In 1990, the United States Environmental Protection Agency indicated that a family of four discharged 300 to 400 gallons of wastewater per day. This amount had almost doubled in 2000. From this wastewater, publicly owned treatment works generated significant amounts of sludge (or “biosolids” as these municipal sludges are now called) that may be disposed of in a variety of ways, including conversion into fertilizers.
There remains a concern, however, with the long term effects of using biosolids in various land use applications, particularly in agriculture intended for human consumption. Possible negative effects may vary with the treatment of the biosolids (e.g., the level of disinfection that was applied to the biosolids prior to its usage). Many commercial biosolids processing technologies produce what is classed by the United States Environmental Protection Agency (“EPA”) as a Class B biosolids, which still has potential pathogens present. The majority of biosolids processed in the United States are still processed using Class B type protocols.
Class A type protocols are particularly desirable, however, because there are significantly increased opportunities for use of Class A biosolids. Known processes for achieving Class A pathogen densities in biosolids are generally costly, and in some instances, cost prohibitive. Thus, it is desirable to develop a low-cost method of biosolids treatment for producing biosolids that will meet or exceed Class A standards.